Rotary fluid handling machines, such as turbines, employ a rotor to recover energy from a working fluid and transfer the energy from a working chamber to a use point. The rotor is comprised of a rotatable member which rotates relative to a fixed member. The rotor may be either a rotatable shaft for rotation within a fixed support or housing which extends axially along and circumferentially around the shaft or it may be a rotatable element extending axially along and circumferentially around a fixed shaft for rotation around the fixed shaft. Generally bearings are used to keep the rotor in alignment. Such bearings are generally lubricated by a liquid lubricant which is generally petroleum based.
It is important that such lubricant be prevented from entering the working chamber of the fluid handling machine and mix with the working fluid as this would reduce the efficiency of the energy transfer from the working fluid and would also result in loss of lubricant.
In order to prevent lubricant from entering the rotary machine working chamber a sealing device may be interposed between the lubricated bearing and the working chamber. One type of sealing device is a contact-type seal wherein the seal apparatus fits between and is in contact with both rotating and fixed elements. However, contact-type seals, also known as rubbing or sliding type seals, generally cannnot be employed in high speed rotary machines, which operate at speeds at or above 1000 rpm, because such seals would wear rapidly and/or fuse with the rotating element due to the high temperatures generated by the rubbing surfaces. In such high speed rotary machines clearance-type seals which do not require contact with a moving surface are more generally used.
A clearance-type seal comprises a narrow spacing between the rotatable and fixed members along at least a portion of their axial length. This narrow spacing is between the lubricated bearing and the working chamber along an axial direction. A gas is introduced to the narrow spacing and flows toward the lubricated bearing. Lubricant from the bearing which flows along on both the rotating and fixed surfaces is prevented from entering into the narrow spacing by the flow of this sealing gas flowing therefrom. The seal may be made more effective by a series of grooves in the shaft surface which serve to minimize gas leakage by the imposition of a flow restriction. Such a seal employing the series of grooves is generally termed a labyrinth seal.
Lubricant from the bearing flows on both the rotating and fixed surfaces toward the sealing gas flow. Lubricant on the rotating surface is hindered from entering the narrow spacing between the shaft and the housing due to the inertial forces which arise, and such lubricant, with the help of the sealing gas flow, is guided into a lubricant collection device, which is generally a recess in the housing, and from there may be collected for reuse. However, lubricant flowing on the non-rotating or fixed surface is not hindered by inertial forces from flowing toward the narrow spacing and a small amount may enter the narrow spacing in spite of the sealing gas flow. This movement by capillary action of the liquid lubricant along the non-rotating surface may result in some lubricant passing into the working chamber of the fluid handling machine.
While the leakage of a small amount of lubricant into the working chamber may not pose significant difficulties in some applications, when the fluid handling machine is employed in a cryogenic operation, especially in cryogenic air separation, such lubricant leakage may create severe problems. For example, such lubricant may solidify at the cold temperatures employed resulting in reduced heat transfer and possibly even blocked flow passages. Furthermore, occasional plant thawing might extend the lubricant throughout the cryogenic plant and may result in a lubricant deposit in an area where fire or explosion hazard is substantial. It is therefore desirable to provide a clearance-type seal for use with high speed rotary fluid handling machines in a cryogenic plant which stops virtually all lubricant from entering the working chamber.
It is therefore an object of this invention to provide an improved clearance-type seal.
It is another object of this invention to provide an improved clearance-type seal which effectively stops lubricant on the non-rotating surface of a rotary fluid handling machine from flowing by capillary action along the non-rotating surface past the seal.